WO2013187276A1 - Secondary battery - Google Patents

Secondary battery Download PDF

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Publication number
WO2013187276A1
WO2013187276A1 PCT/JP2013/065375 JP2013065375W WO2013187276A1 WO 2013187276 A1 WO2013187276 A1 WO 2013187276A1 JP 2013065375 W JP2013065375 W JP 2013065375W WO 2013187276 A1 WO2013187276 A1 WO 2013187276A1
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Prior art keywords
secondary battery
positive electrode
active material
electrode active
peak
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PCT/JP2013/065375
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French (fr)
Japanese (ja)
Inventor
小林　憲司
井上　和彦
信作 齊藤
畠山　大
木村　英和
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日本電気株式会社
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Priority to JP2014521273A priority Critical patent/JP6135667B2/en
Publication of WO2013187276A1 publication Critical patent/WO2013187276A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • This embodiment relates to a secondary battery.
  • Secondary batteries can achieve high energy density, and are therefore widely used as power sources for mobile phones and laptop computers.
  • a lithium ion secondary battery for an electric vehicle, a stationary power storage system, etc.
  • studies on increasing the size of the lithium ion secondary battery have been promoted.
  • a lithium ion secondary battery is used for an electric vehicle, a stationary power storage system, etc., a long life is required. Therefore, development of a secondary battery that does not decrease its capacity even after repeated charge / discharge cycles is required.
  • a carbon material is used for the negative electrode
  • a lithium-containing composite oxide is used for the positive electrode
  • a nonaqueous electrolytic solution is used for the electrolytic solution.
  • a spinel oxide containing manganese with high safety is used for a positive electrode active material included in a positive electrode of a large-sized lithium ion secondary battery.
  • Patent Document 1 0.1 to 4% by mass of 1,3-propane sultone and / or 1,4-butane sultone is contained in an electrolytic solution mainly composed of cyclic carbonate and chain carbonate. A secondary battery including the same is disclosed. Thereby, it is said that a protective film is formed on the surface of the negative electrode and has an effect of suppressing decomposition of the electrolytic solution.
  • Patent Documents 2 and 3 disclose that the same effect can be obtained even when a chain disulfonic acid ester is used.
  • Patent Documents 4 and 5 disclose that a film having high ion conductivity can be obtained on the positive electrode by using a cyclic sulfonic acid ester having mainly two sulfonyl groups as an additive.
  • the positive electrode active material is an oxide containing manganese
  • elution of manganese can be suppressed and the eluted manganese can be prevented from adhering to the negative electrode.
  • Patent Documents 1 to 3 have a low effect of reducing manganese elution. Further, in the methods described in Patent Documents 4 and 5, the effect of reducing the elution of manganese has not been confirmed. In particular, it is described in XPS (X-ray Photoelectron Spectroscopy) analysis that the film is specified by the presence of a sulfur peak near 164.0 eV, but this peak position does not necessarily match the effect of reducing manganese elution.
  • XPS X-ray Photoelectron Spectroscopy
  • This embodiment is intended to provide a secondary battery having a high capacity maintenance rate associated with a cycle.
  • the secondary battery according to the present embodiment includes a lithium salt, an electrolytic solution containing a non-aqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium, and a negative electrode.
  • a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the sulfur K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material.
  • a method for manufacturing a secondary battery according to the present embodiment includes a lithium salt, an electrolyte solution containing a non-aqueous solvent capable of dissolving the lithium salt, and an additive, and a positive electrode containing a positive electrode active material capable of inserting and removing lithium. And a step of assembling a pre-charge / discharge secondary battery comprising a negative electrode and a step of charging / discharging the pre-charge / discharge secondary battery, and the charge / discharge causes sulfur K absorption on the surface of the positive electrode active material.
  • a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the edge X-ray absorption fine structure spectrum is formed.
  • a secondary battery with a high capacity maintenance rate accompanying a cycle is provided.
  • the present inventors diligently studied to solve the above-mentioned problems, and as a result, the X-ray absorption fine structure (hereinafter referred to as “XAFS”) of sulfur near the surface of the positive electrode active material of the secondary battery is X-ray absorption structure.
  • XAFS X-ray absorption fine structure
  • the elution amount of manganese is greatly reduced, and the decrease in the capacity retention rate associated with the cycle is suppressed. I found out.
  • the secondary battery according to the present embodiment includes a lithium salt, an electrolytic solution containing a non-aqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium,
  • a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material.
  • a stable protective film is formed on the positive electrode active material, and the elution of manganese in the charge / discharge cycle is greatly suppressed, and the oxidative decomposition of the electrolyte is suppressed. Improvement effect is obtained.
  • FIG. 1 shows an example of the secondary battery according to this embodiment.
  • the positive electrode 15 includes a positive electrode active material-containing layer 12 containing a positive electrode active material and a positive electrode current collector 11.
  • the negative electrode 16 includes a negative electrode active material-containing layer 14 containing a negative electrode active material, and a negative electrode current collector 13.
  • the positive electrode 15 and the negative electrode 16 are disposed to face each other with a separator 17 interposed therebetween.
  • An electrolyte solution (not shown) is held by the positive electrode 15, the negative electrode 16 and the separator 17.
  • the positive electrode active material according to the present embodiment is not particularly limited as long as it is a positive electrode active material into which lithium can be inserted and desorbed.
  • a Li-containing composite oxide having an average discharge potential near 4 V with respect to Li metal is used. be able to.
  • the positive electrode active material preferably contains manganese, and more preferably contains lithium manganate and lithium nickelate.
  • the lithium manganate is preferably a compound represented by the following formula (1).
  • the compound represented by the following formula (1) has a spinel structure.
  • 0 ⁇ x ⁇ 0.15 is preferable
  • 0 ⁇ x ⁇ 0.13 is more preferable
  • 0 ⁇ x ⁇ 0.1 is more preferable.
  • 0 ⁇ ⁇ ⁇ 0.25 is preferable
  • 0 ⁇ ⁇ ⁇ 0.23 is more preferable
  • 0 ⁇ ⁇ ⁇ 0.2 is further preferable.
  • a part of the site where Mn or O exists may be substituted with another element.
  • the Mn site may be appropriately substituted with another element.
  • examples of other elements include Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Sr, Y, Zr, Nb, In, Sn, La, Ce, Nd, Sm, Gd, Ta, Bi, Pb etc. are mentioned.
  • the Mn site may be substituted with one or more of these elements.
  • the O site may be substituted with another element.
  • examples of other elements include F and Cl.
  • the O site may be substituted with one of these elements or may be substituted with two.
  • the lithium nickelate is preferably a compound represented by the following formula (2).
  • M includes at least one of Al and Mn. 0.10 ⁇ ⁇ ⁇ 0.47, 0.03 ⁇ ⁇ ⁇ 0.4, and 0.13 ⁇ ⁇ + ⁇ ⁇ 0.50. 0.12 ⁇ ⁇ ⁇ 0.40 is preferable, 0.13 ⁇ ⁇ ⁇ 0.35 is more preferable, and 0.15 ⁇ ⁇ ⁇ 0.30 is still more preferable. 0.04 ⁇ ⁇ ⁇ 0.3 is preferable, 0.045 ⁇ ⁇ ⁇ 0.25 is more preferable, and 0.05 ⁇ ⁇ ⁇ 0.2 is even more preferable.
  • the mixing ratio of the compound represented by the formula (1) and the compound represented by the formula (2) contained in the positive electrode active material is the compound represented by the formula (1) and the compound represented by the formula (2).
  • the mass ratio of the compound represented by the formula (1) with respect to the total is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and more preferably 15% by mass to 30%. A mass% or less is more preferable.
  • a method for producing the positive electrode is not particularly limited.
  • the positive electrode active material, a binder, a conductivity imparting agent, and a solvent are mixed to prepare a slurry, and the slurry is applied to the positive electrode current collector, Can be produced by drying.
  • binder resin binders that are usually used according to characteristics that are important as secondary batteries, such as rate characteristics, low temperature discharge characteristics, pulse discharge characteristics, energy density, weight reduction, and miniaturization, can be used as appropriate.
  • binder for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like can be used. These may use 1 type and may use 2 or more types together.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • the conductivity imparting agent for example, acetylene black, carbon or the like can be used. These may use 1 type and may use 2 or more types together.
  • solvent N-methyl-2-pyrrolidone (NMP) or the like can be used.
  • NMP N-methyl-2-pyrrolidone
  • positive electrode current collector an aluminum metal foil or the like is preferably used.
  • the negative electrode active material contained in the negative electrode according to the present embodiment is not particularly limited, but a carbon material that can insert and desorb Li ions is preferable. Further, a metal alloyed with Li, a metal oxide, a composite material of these and a carbon material, or a transition metal nitride can also be used. From the viewpoint of improving high rate characteristics and output characteristics, the negative electrode active material is preferably amorphous carbon.
  • the method for producing the negative electrode is not particularly limited.
  • the negative electrode active material, a binder, and a solvent are mixed to prepare a slurry, the slurry is applied to a negative electrode current collector, and the solvent is dried. can do.
  • the binder is appropriately selected according to the characteristics that are important for the secondary battery.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • a rubber binder can also be used. These may use 1 type and may use 2 or more types together.
  • NMP N-methyl-2-pyrrolidone
  • As the negative electrode current collector a copper foil or the like is preferably used.
  • the separator according to the present embodiment is not particularly limited, and for example, a porous separator such as a woven fabric, a glass fiber, or a porous synthetic resin film can be used. Specifically, a polyolefin film such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used.
  • the electrolytic solution according to the present embodiment includes a lithium salt, a nonaqueous solvent capable of dissolving the lithium salt, and an additive.
  • the lithium salt is a supporting salt is not particularly limited, for example LiBF 4, LiPF 6, LiClO 4 , LiAsF 6, LiSbF 6, LiCF 3 SO 3, Li (CF 3 SO 2) N, LiC 4 F 9 SO 3 , Li (CF 3 SO 2 ) 3 C, Li (C 2 F 5 SO 2 ) 2 N, and the like. These may use 1 type and may use 2 or more types together. In particular, it is preferable that the lithium salt contains LiPF 6 .
  • the concentration of the lithium salt in the electrolytic solution can be, for example, 0.8 to 1.5 mol / l. Further, it is preferably 0.9 to 1.2 mol / l.
  • non-aqueous solvent a non-aqueous solvent capable of dissolving a lithium salt usually used as an aprotic solvent can be appropriately selected and used.
  • a lithium salt may be dissolved by 0.5 mol / L or more.
  • the non-aqueous solvent for example, cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, chlorinated hydrocarbons, cyclic ethers, chain ethers, ketones, nitriles and the like can be used.
  • EC ethylene carbonate
  • PC propylene carbonate
  • GBL ⁇ -butyrolactone
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • esters esters
  • the additive refers to a compound that can form a stable protective film on the positive electrode active material by charging and discharging.
  • the additive is not particularly limited as long as it is a compound that can form a stable protective film on the positive electrode active material by charging and discharging, but the use of a chain disulfonic acid ester in the initial cycle (cycle number: 1 to 5 times) It is preferable from the viewpoint that a protective film is stably formed on the positive electrode active material at this stage.
  • the negative electrode film is formed by a reduction reaction, the positive electrode film is considered to be formed by deprotonation. Therefore, the additive is preferably a chain disulfonic acid ester whose terminal is a carbon-carbon double bond.
  • the chain disulfonic acid ester having a carbon-carbon double bond at the end is preferably a chain disulfonic acid ester having both ends at a carbon-carbon double bond.
  • Examples of the chain disulfonic acid ester whose both ends are carbon-carbon double bonds include a compound represented by the following formula (3).
  • the chain disulfonic acid ester preferably does not contain a sterically large structure such as a benzene ring.
  • the amount of the additive contained in the electrolytic solution is preferably 1% by mass or more and 5% by mass or less based on the mass of the electrolytic solution. By being 5 mass% or less, an additive can fully be dissolved in electrolyte solution and the viscosity of electrolyte solution can be made low. From the viewpoint of obtaining a sufficient film effect, the amount of the additive contained in the electrolytic solution is more preferably 1.5% by mass or more and 4% by mass or less based on the mass of the electrolytic solution. More preferably, it is 2 mass% or more and 3 mass% or less.
  • a cyclic sulfonic acid ester that easily forms a protective film on the negative electrode may be further mixed with the electrolytic solution.
  • the mixing ratio of the additive and the cyclic sulfonic acid ester is not particularly limited, but it is preferable to add them in a range in which the total amount of both does not exceed 5% by mass with respect to the electrolytic solution.
  • the protective film in a positive electrode is hard to be formed only with cyclic sulfonate ester, sufficient effect is not acquired.
  • a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material.
  • the compound preferably has a peak in the range of 2476.5 eV or more and 2478.9 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur, and may have a peak in the range of 2477 eV or more and 2478.7 eV or less. More preferably, it has a peak in the range of 2477.5 eV or more and 2478.5 eV or less.
  • the surface of the positive electrode active material indicates a region of 100 nm in the depth direction from the outermost surface of the positive electrode active material.
  • the measurement method of the K absorption edge X-ray absorption fine structure (XAFS) (X-ray Absorption Fine Structure) spectrum of sulfur is described below.
  • the K absorption edge XAFS spectrum of sulfur was measured at synchrotron radiation experiment facilities such as the beam line 9A (soft X-ray mode) of the Synchrotron Radiation Science Research Facility (Photon Factory), Institute for Materials Structure Science, High Energy Accelerator Research Organization It is.
  • the energy dependence of the fluorescent X-rays and secondary electrons emitted from the sample is measured.
  • the K absorption edge XAFS spectrum of is obtained.
  • a conversion electron yield method for detecting secondary electrons emitted from the sample information on the depth from the outermost surface of the sample to about 100 nm is obtained. If fluorescent X-rays emitted from the sample are detected, information about a depth of about 1 ⁇ m can be obtained from the outermost surface of the sample.
  • the absolute value of the energy position of the obtained spectrum can be determined based on a standard sample.
  • Na 2 SO 4 is used as a standard sample, and the energy calibration is performed with the peak position of Na 2 SO 4 being 2480 eV.
  • the energy position indicating the maximum value of the peak intensity of the sulfur K absorption edge XAFS spectrum in the present embodiment is 1 eV or more and 2 eV or less on the low energy side with respect to the energy position indicating the maximum value of the peak intensity of Na 2 SO 4. It is preferably located at a low energy side of 1.1 eV or more and 1.9 eV or less, more preferably 1.2 eV or more and 1.8 eV or less. More preferably, it is particularly preferably 1.3 eV or more and 1.7 eV or less on the low energy side.
  • the amount of the protective film can be estimated.
  • the XAFS measurement of a positive electrode can be performed also at the K absorption edge of phosphorus. This measurement method is the same as the measurement of sulfur K absorption edge XAFS.
  • the elution amount of manganese it can measure by quantifying the manganese deposited on the negative electrode using a wavelength dispersion type fluorescent X-ray analyzer.
  • the peak in the XAFS spectrum can be specified by the following method.
  • (1) The peak position is specified from the second derivative of the measurement data.
  • (3) The function of (2) is fitted with a plurality of functions of the peak position of (1). (Functions are generally Lorentz functions and Pseudo-voice functions.) (4) When the half width of (3) is less than the spectral resolution (excitation lifetime), it is determined as noise.
  • the shape of the secondary battery according to the present embodiment is not particularly limited, but various shapes such as a square shape, a paper shape, a laminated shape, a cylindrical shape, a coin shape, and a laminated exterior shape can be employed.
  • a method for manufacturing a secondary battery according to the present embodiment includes a lithium salt, an electrolyte solution containing a non-aqueous solvent capable of dissolving the lithium salt, and an additive, and a positive electrode containing a positive electrode active material capable of inserting and removing lithium. And a step of assembling a pre-charge / discharge secondary battery comprising a negative electrode and a step of charging / discharging the pre-charge / discharge secondary battery, and the charge / discharge causes sulfur K absorption on the surface of the positive electrode active material.
  • a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the edge X-ray absorption fine structure spectrum is formed.
  • a positive electrode 15 and a negative electrode 16 are laminated via a separator 17 in a dry air or inert gas atmosphere to produce a laminated electrode body.
  • the laminated electrode body may be wound.
  • the laminated electrode body is accommodated in a battery can or an exterior body (not shown) such as a flexible film made of a laminated body of synthetic resin and metal foil.
  • an electrolytic solution is poured into the exterior body, the laminated electrode body is impregnated with the electrolytic solution, and the exterior body is sealed. Thereby, the secondary battery before charging / discharging is produced.
  • the protective film formed on the positive electrode active material of the positive electrode includes a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur.
  • Example 1 Preparation of secondary battery before charge / discharge
  • carbon black as a conductivity-imparting agent
  • the mixture was uniformly dispersed in NMP in which PVDF as a binder was dissolved to prepare a slurry.
  • the slurry was applied on an aluminum metal foil (thickness 20 ⁇ m), which was a positive electrode current collector.
  • the positive electrode was produced by evaporating NMP.
  • LiPF 6 as a supporting salt, an EC / DEC solvent (EC: DEC 30: 70 (volume ratio)), and the above formula (Terminal as a additive) is a chain disulfonic acid ester having a carbon-carbon double bond ( The compound shown by 3) was mixed to prepare an electrolytic solution.
  • the concentration of LiPF 6 in the electrolytic solution was 1 mol / L.
  • strand-shaped disulfonic acid ester in electrolyte solution was 2 mass% with respect to the mass of electrolyte solution.
  • the positive electrode and the negative electrode were laminated via a polyethylene separator to produce a laminated electrode body.
  • the laminated electrode body was wrapped with aluminum laminate, and the three sides around the aluminum laminate were heat-sealed. Before heat-sealing the last side, the electrolyte solution was poured into an aluminum laminate, and the laminated electrode body was impregnated with the electrolyte solution. Then, the secondary battery before charging / discharging was produced by heat-seal
  • Capacity maintenance rate The ratio of the discharge capacity after 1000 cycles of the cycle test to the discharge capacity after 1 cycle test was calculated as the capacity retention rate.
  • X-ray fluorescence analysis (X-ray fluorescence analysis (XRF)) After 1000 cycle tests, the negative electrode was thoroughly washed with DEC. Thereafter, the negative electrode was cut into a size of 1 cm ⁇ 1 cm as a sample for analysis. After sealing in a laminate pack, the analysis sample was subjected to a quantitative analysis of manganese using a fluorescent X-ray analyzer (Rh K ⁇ ray, 60 kV 66 mA, spectral crystal LiF (200), manufactured by Panalical).
  • a fluorescent X-ray analyzer Rh K ⁇ ray, 60 kV 66 mA, spectral crystal LiF (200), manufactured by Panalical.
  • Example 1 A secondary battery before charge / discharge was prepared in the same manner as in Example 1 except that an electrolyte was prepared using a compound represented by the following formula (4) whose terminal is a chain disulfonic acid ester having a benzene ring as an additive. A cycle test and various measurements were performed.
  • FIG. 2 shows the result of XAFS measurement at the sulfur K absorption edge
  • FIG. 3 shows the result of XAFS measurement at phosphorus K absorption edge.
  • FIG. 3 shows the results of measurement of the phosphorus K absorption edge XAFS spectrum.
  • the decomposition state of the electrolyte was examined by performing XAFS measurement at the phosphorus K absorption edge, which is the main component of the electrolyte.
  • the peak B existing at 2155 to 2160 eV corresponds to trifluorophosphoric acid (PF 6 ) which is a supporting salt contained in the electrolytic solution.
  • the peak A existing at 2150 to 2155 eV corresponds to POF 3 having a reduced degree of fluorination produced by decomposition of PF 6 in the electrolytic solution.
  • Table 1 shows the intensity ratio (A / B) between the peak A and the peak B after 100 cycles.
  • the ratio of peak A which is a peak derived from the decomposition component of PF 6 in the electrolyte
  • Example 1 in which peaks exist at 2476 to 2479 eV, the ratio of peak A, which is a peak derived from the decomposition component of PF 6 in the electrolyte, is low.
  • Example 1 the intensity ratio (Example 1 / Comparative Example 1) of manganese of Example 1 and Comparative Example 1 was 0.86. Therefore, it was confirmed that the amount of precipitation of manganese in the negative electrode, that is, the amount of manganese elution from the positive electrode was reduced in Example 1 compared to Comparative Example 1. In addition, since the amount of manganese elution was very small, a sample after 1000 cycles was used for measurement, and the strength ratio of the two was compared.
  • Example 1 had a higher capacity retention rate than Comparative Example 1.
  • Example 1 the elution of manganese from the positive electrode is suppressed, which is considered to be because the oxidative decomposition of the electrolytic solution component is reduced.

Abstract

A secondary battery with a high capacitance retention rate associated with charge/discharge cycles is provided. This secondary battery is equipped with: an electrolytic solution that contains a lithium salt, a non-aqueous solvent capable of dissolving the lithium salt, and an additive; a positive electrode that contains a positive electrode active material into/from which lithium can be inserted/removed; and a negative electrode. A compound that has a peak in the 2,476eV to 2,479eV range of a sulfur K-edge X-ray absorption fine structure spectrum is formed on a surface of the positive electrode active material.

Description

二次電池Secondary battery
　本実施形態は二次電池に関する。 This embodiment relates to a secondary battery.
　二次電池、特にリチウムイオン二次電池は、高いエネルギー密度を実現できることから、携帯電話やノートパソコン等の電源用として広く普及している。近年では、リチウムイオン二次電池を電動車両、定置用蓄電システム等に使用するために、リチウムイオン二次電池の大型化に関する検討がすすめられている。リチウムイオン二次電池を電動車両、定置用蓄電システム等に使用する場合、長い寿命が必要とされる。したがって、充放電サイクルを繰り返しても容量低下しない二次電池の開発が求められている。 Secondary batteries, particularly lithium ion secondary batteries, can achieve high energy density, and are therefore widely used as power sources for mobile phones and laptop computers. In recent years, in order to use a lithium ion secondary battery for an electric vehicle, a stationary power storage system, etc., studies on increasing the size of the lithium ion secondary battery have been promoted. When a lithium ion secondary battery is used for an electric vehicle, a stationary power storage system, etc., a long life is required. Therefore, development of a secondary battery that does not decrease its capacity even after repeated charge / discharge cycles is required.
　リチウムイオン二次電池は、負極には炭素材料が用いられ、正極にはリチウム含有複合酸化物が用いられ、電解液には非水電解液が用いられる。特に、大型用のリチウムイオン二次電池の正極に含まれる正極活物質には、安全性の高いマンガンを含むスピネル酸化物が用いられる。しかしながら、充放電サイクルに伴いマンガンが電解液に溶出し、負極に付着して二次電池の容量低下を引き起こす課題がある。 In the lithium ion secondary battery, a carbon material is used for the negative electrode, a lithium-containing composite oxide is used for the positive electrode, and a nonaqueous electrolytic solution is used for the electrolytic solution. In particular, a spinel oxide containing manganese with high safety is used for a positive electrode active material included in a positive electrode of a large-sized lithium ion secondary battery. However, there is a problem that manganese elutes into the electrolytic solution along with the charge / discharge cycle and adheres to the negative electrode, causing a reduction in capacity of the secondary battery.
　前記課題を解決する方法として様々な技術が提案されている。例えば、特許文献１には、環状カーボネート及び鎖状カーボネートを主成分とする電解液中に、０．１質量％以上４質量％以下の１，３－プロパンスルトン及び／又は１，４－ブタンスルトンを含む二次電池が開示されている。これにより、負極の表面に保護皮膜が形成されて電解液の分解を抑制する効果があるとされている。また、特許文献２及び３では、鎖状ジスルホン酸エステルを用いても同様の効果が得られることが開示されている。 Various techniques have been proposed as a method for solving the above problems. For example, in Patent Document 1, 0.1 to 4% by mass of 1,3-propane sultone and / or 1,4-butane sultone is contained in an electrolytic solution mainly composed of cyclic carbonate and chain carbonate. A secondary battery including the same is disclosed. Thereby, it is said that a protective film is formed on the surface of the negative electrode and has an effect of suppressing decomposition of the electrolytic solution. Patent Documents 2 and 3 disclose that the same effect can be obtained even when a chain disulfonic acid ester is used.
　また、特許文献４及び５には、主にスルホニル基を２個有する環式スルホン酸エステルを添加剤として用いることにより、正極にもイオン伝導性の高い皮膜が得られることが開示されている。これにより、正極活物質がマンガンを含む酸化物の場合にも、マンガンの溶出を抑え、溶出したマンガンが負極に付着するのを防ぐことができることが記載されている。 Patent Documents 4 and 5 disclose that a film having high ion conductivity can be obtained on the positive electrode by using a cyclic sulfonic acid ester having mainly two sulfonyl groups as an additive. Thus, it is described that even when the positive electrode active material is an oxide containing manganese, elution of manganese can be suppressed and the eluted manganese can be prevented from adhering to the negative electrode.
特開２０００－３７２４号公報Japanese Patent Laid-Open No. 2000-3724 特開２０００－１３３３０４号公報JP 2000-133304 A 米国特許第６４３６５８２号明細書US Pat. No. 6,436,582 特許第４３４５６４２号公報Japanese Patent No. 4345642 特開２００６－１５６３１４号公報JP 2006-156314 A
　しかしながら、特許文献１から３に記載の方法では、マンガンの溶出を低減する効果は低い。また、特許文献４及び５に記載の方法では、マンガンの溶出低減の効果は確認されていない。特に、ＸＰＳ（Ｘ－ｒａｙ　Ｐｈｏｔｏｅｌｅｃｔｒｏｎ　Ｓｐｅｃｔｒｏｓｃｏｐｙ）分析において１６４．０ｅＶ付近の硫黄のピークの存在により皮膜を特定する旨が記載されているが、このピーク位置とマンガン溶出低減の効果とは必ずしも一致しない。 However, the methods described in Patent Documents 1 to 3 have a low effect of reducing manganese elution. Further, in the methods described in Patent Documents 4 and 5, the effect of reducing the elution of manganese has not been confirmed. In particular, it is described in XPS (X-ray Photoelectron Spectroscopy) analysis that the film is specified by the presence of a sulfur peak near 164.0 eV, but this peak position does not necessarily match the effect of reducing manganese elution.
　本実施形態は、サイクルに伴う容量維持率の高い二次電池を提供することを目的とする。 This embodiment is intended to provide a secondary battery having a high capacity maintenance rate associated with a cycle.
　本実施形態に係る二次電池は、リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える二次電池であって、前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成されている。 The secondary battery according to the present embodiment includes a lithium salt, an electrolytic solution containing a non-aqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium, and a negative electrode. A compound having a peak in the range of 2476 eV or more and 2479 eV or less in the sulfur K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material.
　本実施形態に係る二次電池の製造方法は、リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える充放電前二次電池を組み立てる工程と、前記充放電前二次電池を充放電する工程と、を含み、前記充放電により、前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成される。 A method for manufacturing a secondary battery according to the present embodiment includes a lithium salt, an electrolyte solution containing a non-aqueous solvent capable of dissolving the lithium salt, and an additive, and a positive electrode containing a positive electrode active material capable of inserting and removing lithium. And a step of assembling a pre-charge / discharge secondary battery comprising a negative electrode and a step of charging / discharging the pre-charge / discharge secondary battery, and the charge / discharge causes sulfur K absorption on the surface of the positive electrode active material. A compound having a peak in the range of 2476 eV or more and 2479 eV or less in the edge X-ray absorption fine structure spectrum is formed.
　本実施形態によれば、サイクルに伴う容量維持率の高い二次電池が提供される。 According to this embodiment, a secondary battery with a high capacity maintenance rate accompanying a cycle is provided.
本実施形態に係る二次電池の一例を示す断面図である。It is sectional drawing which shows an example of the secondary battery which concerns on this embodiment. 実施例１及び比較例１の正極、並びに標準試料（Ｎａ２ＳＯ４）の硫黄のＫ吸収端ＸＡＦＳスペクトルを示す図である。The positive electrode of Example 1 and Comparative Example 1, and illustrates the K-edge XAFS spectrum of sulfur standard sample (Na 2 SO 4). 実施例１及び比較例１の正極の、各サイクル後におけるリンのＫ吸収端ＸＡＦＳスペクトルを示す図である。It is a figure which shows the K absorption edge XAFS spectrum of the phosphorus after each cycle of the positive electrode of Example 1 and Comparative Example 1.
　本発明者らは、前記課題を解決すべく鋭意検討したところ、二次電池の正極活物質表面付近の硫黄のＫ吸収端Ｘ線吸収微細構造（Ｘ－ｒａｙ　ａｂｓｏｒｐｔｉｏｎ　ｆｉｎｅ　ｓｔｒｕｃｔｕｒｅ、以下、「ＸＡＦＳ」と称する。）スペクトルにおいて、サイクル初期において正極活物質表面付近に硫黄を含有する特定の化合物が存在する場合、マンガンの溶出量が大幅に低減され、サイクルに伴う容量維持率の低下が抑制されることを見出した。 The present inventors diligently studied to solve the above-mentioned problems, and as a result, the X-ray absorption fine structure (hereinafter referred to as “XAFS”) of sulfur near the surface of the positive electrode active material of the secondary battery is X-ray absorption structure. In the spectrum, when a specific compound containing sulfur exists in the vicinity of the surface of the positive electrode active material at the beginning of the cycle, the elution amount of manganese is greatly reduced, and the decrease in the capacity retention rate associated with the cycle is suppressed. I found out.
　すなわち、本実施形態に係る二次電池は、リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える二次電池であって、前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成されている。本実施形態では安定した保護皮膜が正極活物質上に形成されており、充放電サイクルにおけるマンガンの溶出が大幅に抑制され、電解液の酸化分解が抑制されるため、サイクルに伴う容量維持率の向上効果が得られる。 That is, the secondary battery according to the present embodiment includes a lithium salt, an electrolytic solution containing a non-aqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium, In the secondary battery including a negative electrode, a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material. In this embodiment, a stable protective film is formed on the positive electrode active material, and the elution of manganese in the charge / discharge cycle is greatly suppressed, and the oxidative decomposition of the electrolyte is suppressed. Improvement effect is obtained.
　本実施形態に係る二次電池の一例を図１に示す。正極１５は、正極活物質を含有する正極活物質含有層１２と、正極集電体１１とを備える。負極１６は、負極活物質を含有する負極活物質含有層１４と、負極集電体１３とを備える。正極１５と負極１６とはセパレータ１７を介して対向配置されている。不図示の電解液は正極１５、負極１６及びセパレータ１７に保持されている。 FIG. 1 shows an example of the secondary battery according to this embodiment. The positive electrode 15 includes a positive electrode active material-containing layer 12 containing a positive electrode active material and a positive electrode current collector 11. The negative electrode 16 includes a negative electrode active material-containing layer 14 containing a negative electrode active material, and a negative electrode current collector 13. The positive electrode 15 and the negative electrode 16 are disposed to face each other with a separator 17 interposed therebetween. An electrolyte solution (not shown) is held by the positive electrode 15, the negative electrode 16 and the separator 17.
　本実施形態に係る正極活物質は、リチウムを挿入、脱離可能な正極活物質であれば特に限定されないが、例えばＬｉ金属に対して４Ｖ付近に平均放電電位を有するＬｉ含有複合酸化物を用いることができる。正極活物質はマンガンを含むことが好ましく、マンガン酸リチウムとニッケル酸リチウムとを含むことがより好ましい。 The positive electrode active material according to the present embodiment is not particularly limited as long as it is a positive electrode active material into which lithium can be inserted and desorbed. For example, a Li-containing composite oxide having an average discharge potential near 4 V with respect to Li metal is used. be able to. The positive electrode active material preferably contains manganese, and more preferably contains lithium manganate and lithium nickelate.
　前記マンガン酸リチウムとしては、下記式（１）で示される化合物が好ましい。下記式（１）で示される化合物はスピネル構造を有する。 The lithium manganate is preferably a compound represented by the following formula (1). The compound represented by the following formula (1) has a spinel structure.
　　Ｌｉ１＋ｘＭｎ２Ｏ４＋δ　　（１）
　前記式（１）において、０≦ｘ＜０．２、０≦δ＜０．３である。０≦ｘ≦０．１５が好ましく、０≦ｘ≦０．１３がより好ましく、０≦ｘ≦０．１がさらに好ましい。また、０≦δ≦０．２５が好ましく、０≦δ≦０．２３がより好ましく、０≦δ≦０．２がさらに好ましい。 Li 1 + x Mn 2 O 4 + δ (1)
In the formula (1), 0 ≦ x <0.2 and 0 ≦ δ <0.3. 0 ≦ x ≦ 0.15 is preferable, 0 ≦ x ≦ 0.13 is more preferable, and 0 ≦ x ≦ 0.1 is more preferable. Further, 0 ≦ δ ≦ 0.25 is preferable, 0 ≦ δ ≦ 0.23 is more preferable, and 0 ≦ δ ≦ 0.2 is further preferable.
　前記式（１）で示される化合物において、ＭｎまたはＯの存在するサイトの一部は他の元素で置換されていてもよい。例えば、目的とする二次電池の各特性を向上させる観点から、適宜、Ｍｎサイトを他の元素で置換してもよい。他の元素としては、例えば、Ｍｇ、Ａｌ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｏ、Ｎｉ、Ｚｎ、Ｓｒ、Ｙ、Ｚｒ、Ｎｂ、Ｉｎ、Ｓｎ、Ｌａ、Ｃｅ、Ｎｄ、Ｓｍ、Ｇｄ、Ｔａ、Ｂｉ、Ｐｂ等が挙げられる。Ｍｎサイトはこれらの元素のうち一種で置換されてもよく、二種以上で置換されてもよい。また、Ｏサイトを他の元素で置換してもよい。他の元素としては、例えば、Ｆ、Ｃｌ等が挙げられる。Ｏサイトはこれらの元素のうち一種で置換されてもよく、二種で置換されてもよい。 In the compound represented by the formula (1), a part of the site where Mn or O exists may be substituted with another element. For example, from the viewpoint of improving each characteristic of the target secondary battery, the Mn site may be appropriately substituted with another element. Examples of other elements include Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Sr, Y, Zr, Nb, In, Sn, La, Ce, Nd, Sm, Gd, Ta, Bi, Pb etc. are mentioned. The Mn site may be substituted with one or more of these elements. Further, the O site may be substituted with another element. Examples of other elements include F and Cl. The O site may be substituted with one of these elements or may be substituted with two.
　前記ニッケル酸リチウムとしては、下記式（２）で示される化合物が好ましい。 The lithium nickelate is preferably a compound represented by the following formula (2).
　　ＬｉＮｉ１－α－βＣｏαＭβＯ２　　（２）
　前記式（２）において、ＭはＡｌ及びＭｎの少なくとも一方を含む。０．１０≦α≦０．４７、０．０３≦β≦０．４、０．１３≦α＋β≦０．５０である。０．１２≦α≦０．４０が好ましく、０．１３≦α≦０．３５がより好ましく、０．１５≦α≦０．３０がさらに好ましい。０．０４≦β≦０．３が好ましく、０．０４５≦β≦０．２５がより好ましく、０．０５≦β≦０．２がさらに好ましい。０．１５≦α＋β≦０．４０が好ましく、０．１６≦α＋β≦０．３５がより好ましく、０．１７≦α＋β≦０．３０がさらに好ましい。前記式（２）で示される化合物において、Ｏの存在するサイトの一部は他の元素で置換されていてもよい。 LiNi 1-α-β Co α M β O 2 (2)
In the formula (2), M includes at least one of Al and Mn. 0.10 ≦ α ≦ 0.47, 0.03 ≦ β ≦ 0.4, and 0.13 ≦ α + β ≦ 0.50. 0.12 ≦ α ≦ 0.40 is preferable, 0.13 ≦ α ≦ 0.35 is more preferable, and 0.15 ≦ α ≦ 0.30 is still more preferable. 0.04 ≦ β ≦ 0.3 is preferable, 0.045 ≦ β ≦ 0.25 is more preferable, and 0.05 ≦ β ≦ 0.2 is even more preferable. 0.15 ≦ α + β ≦ 0.40 is preferable, 0.16 ≦ α + β ≦ 0.35 is more preferable, and 0.17 ≦ α + β ≦ 0.30 is still more preferable. In the compound represented by the formula (2), a part of the site where O is present may be substituted with another element.
　正極活物質に含まれる前記式（１）で示される化合物と前記式（２）で示される化合物との混合比は、前記式（１）で示される化合物と前記式（２）で示される化合物との合計に対する、前記式（１）で示される化合物の質量比で、５質量％以上、５０質量％以下が好ましく、１０質量％以上、４０質量％以下がより好ましく、１５質量％以上、３０質量％以下がさらに好ましい。 The mixing ratio of the compound represented by the formula (1) and the compound represented by the formula (2) contained in the positive electrode active material is the compound represented by the formula (1) and the compound represented by the formula (2). The mass ratio of the compound represented by the formula (1) with respect to the total is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and more preferably 15% by mass to 30%. A mass% or less is more preferable.
　正極の作製方法は特に限定されないが、例えば、前記正極活物質と、バインダーと、導電性付与剤と、溶媒とを混合してスラリーを調製し、該スラリーを正極集電体に塗布し、溶媒を乾燥することで作製することができる。 A method for producing the positive electrode is not particularly limited. For example, the positive electrode active material, a binder, a conductivity imparting agent, and a solvent are mixed to prepare a slurry, and the slurry is applied to the positive electrode current collector, Can be produced by drying.
　バインダーとしては、レート特性、低温放電特性、パルス放電特性、エネルギー密度、軽量化、小型化等の、二次電池として重視する特性に応じて通常用いられる樹脂系結着剤を適宜用いることができる。バインダーとしては、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等を用いることができる。これらは一種を用いてもよく、二種以上を併用してもよい。導電性付与剤としては、例えばアセチレンブラック、カーボン等を用いることができる。これらは一種を用いてもよく、二種以上を併用してもよい。溶媒としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）等を用いることができる。正極集電体としては、アルミニウム金属箔等を用いることが好ましい。 As the binder, resin binders that are usually used according to characteristics that are important as secondary batteries, such as rate characteristics, low temperature discharge characteristics, pulse discharge characteristics, energy density, weight reduction, and miniaturization, can be used as appropriate. . As the binder, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like can be used. These may use 1 type and may use 2 or more types together. As the conductivity imparting agent, for example, acetylene black, carbon or the like can be used. These may use 1 type and may use 2 or more types together. As the solvent, N-methyl-2-pyrrolidone (NMP) or the like can be used. As the positive electrode current collector, an aluminum metal foil or the like is preferably used.
　本実施形態に係る負極に含まれる負極活物質としては、特に限定されないが、Ｌｉイオンを挿入、脱離可能なカーボン材料が好ましい。また、Ｌｉと合金化する金属、金属酸化物又はそれらとカーボン材料との複合材料、あるいは遷移金属窒化物を用いることもできる。ハイレート特性及び出力特性向上の観点から、負極活物質は非晶質炭素であることが好ましい。 The negative electrode active material contained in the negative electrode according to the present embodiment is not particularly limited, but a carbon material that can insert and desorb Li ions is preferable. Further, a metal alloyed with Li, a metal oxide, a composite material of these and a carbon material, or a transition metal nitride can also be used. From the viewpoint of improving high rate characteristics and output characteristics, the negative electrode active material is preferably amorphous carbon.
　負極の作製方法は特に限定されないが、例えば、前記負極活物質と、バインダーと、溶媒とを混合してスラリーを調製し、該スラリーを負極集電体に塗布し、溶媒を乾燥することで作製することができる。 The method for producing the negative electrode is not particularly limited. For example, the negative electrode active material, a binder, and a solvent are mixed to prepare a slurry, the slurry is applied to a negative electrode current collector, and the solvent is dried. can do.
　バインダーは、二次電池として重視する特性に応じて適宜選択される。例えば、正極のバインダーとして用いられる材料である、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等を用いることができる。また、ゴム系バインダーを用いることもできる。これらは一種を用いてもよく、二種以上を併用してもよい。溶媒としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）等を用いることができる。負極集電体としては、銅箔等を用いることが好ましい。 The binder is appropriately selected according to the characteristics that are important for the secondary battery. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like, which is a material used as a binder for the positive electrode, can be used. A rubber binder can also be used. These may use 1 type and may use 2 or more types together. As the solvent, N-methyl-2-pyrrolidone (NMP) or the like can be used. As the negative electrode current collector, a copper foil or the like is preferably used.
　本実施形態に係るセパレータは特に限定されないが、例えば織布、硝子繊維、多孔性合成樹脂膜等の多孔質セパレータを用いることができる。具体的には、ポリプロピレン、ポリエチレン等のポリオレフィン、フッ素樹脂等の多孔性フィルムを用いることができる。 The separator according to the present embodiment is not particularly limited, and for example, a porous separator such as a woven fabric, a glass fiber, or a porous synthetic resin film can be used. Specifically, a polyolefin film such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used.
　本実施形態に係る電解液は、リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む。 The electrolytic solution according to the present embodiment includes a lithium salt, a nonaqueous solvent capable of dissolving the lithium salt, and an additive.
　支持塩であるリチウム塩としては、特に限定されないが、例えばＬｉＢＦ４、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＣＦ３ＳＯ３、Ｌｉ（ＣＦ３ＳＯ２）Ｎ、ＬｉＣ４Ｆ９ＳＯ３、Ｌｉ（ＣＦ３ＳＯ２）３Ｃ、Ｌｉ（Ｃ２Ｆ５ＳＯ２）２Ｎ等が挙げられる。これらは一種を用いてもよく、二種以上を併用してもよい。特に、リチウム塩がＬｉＰＦ６を含むことが好ましい。電解液中のリチウム塩の濃度は、例えば０．８～１．５ｍｏｌ／ｌとすることができる。また、０．９～１．２ｍｏｌ／ｌであることが好ましい。 The lithium salt is a supporting salt is not particularly limited, for example LiBF 4, LiPF 6, LiClO 4 , LiAsF 6, LiSbF 6, LiCF 3 SO 3, Li (CF 3 SO 2) N, LiC 4 F 9 SO 3 , Li (CF 3 SO 2 ) 3 C, Li (C 2 F 5 SO 2 ) 2 N, and the like. These may use 1 type and may use 2 or more types together. In particular, it is preferable that the lithium salt contains LiPF 6 . The concentration of the lithium salt in the electrolytic solution can be, for example, 0.8 to 1.5 mol / l. Further, it is preferably 0.9 to 1.2 mol / l.
　非水溶媒としては、非プロトン性溶媒として通常用いられるリチウム塩を溶解可能な非水溶媒から適宜選択して用いることができる。非水溶媒は、例えばリチウム塩を０．５ｍｏｌ／Ｌ以上溶解すればよい。非水溶媒としては、例えば、環状カーボネート類、鎖状カーボネート類、脂肪族カルボン酸エステル類、塩素化炭化水素、環状エーテル類、鎖状エーテル類、ケトン類、ニトリル類等を用いることができる。さらに具体的には、高誘電率溶媒としてエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）及びγ－ブチロラクトン（ＧＢＬ）からなる群から選択される少なくとも１種と、低粘度溶媒としてジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）及びエステル類からなる群から選択される少なくとも１種とを混合した混合液を用いることが好ましい。該混合液としては、例えばＥＣ／ＤＥＣ、ＰＣ／ＤＭＣ、ＰＣ／ＥＣ／ＤＥＣ等の混合液が好ましい。なお、溶媒の純度が低い場合には、電位窓が高電位側に広い溶媒種の混合比率を高めることが好ましい。 As the non-aqueous solvent, a non-aqueous solvent capable of dissolving a lithium salt usually used as an aprotic solvent can be appropriately selected and used. As the non-aqueous solvent, for example, a lithium salt may be dissolved by 0.5 mol / L or more. As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, chlorinated hydrocarbons, cyclic ethers, chain ethers, ketones, nitriles and the like can be used. More specifically, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and γ-butyrolactone (GBL) as a high dielectric constant solvent, and diethyl carbonate (DEC) as a low viscosity solvent. It is preferable to use a mixed solution obtained by mixing at least one selected from the group consisting of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and esters. As the mixed solution, for example, a mixed solution of EC / DEC, PC / DMC, PC / EC / DEC or the like is preferable. In addition, when the purity of the solvent is low, it is preferable to increase the mixing ratio of solvent types having a wide potential window on the high potential side.
　本実施形態において添加剤とは、充放電により正極活物質上に安定な保護皮膜を形成できる化合物を示す。添加剤としては、充放電により正極活物質上に安定な保護皮膜を形成できる化合物であれば特に限定されないが、鎖状ジスルホン酸エステルを用いることが、サイクル初期（サイクル回数：１～５回）の段階で正極活物質上に安定して保護皮膜が形成される観点から好ましい。また、負極の皮膜は還元反応により形成されるが、正極の皮膜は脱プロトンによる吸着により形成されると考えられる。したがって、添加剤としては、末端が炭素－炭素二重結合である鎖状ジスルホン酸エステルであることが好ましい。また、末端が炭素－炭素二重結合である鎖状ジスルホン酸エステルとしては、両末端が炭素－炭素二重結合である鎖状ジスルホン酸エステルが好ましい。両末端が炭素－炭素二重結合である鎖状ジスルホン酸エステルとしては、例えば下記式（３）で示される化合物が挙げられる。 In the present embodiment, the additive refers to a compound that can form a stable protective film on the positive electrode active material by charging and discharging. The additive is not particularly limited as long as it is a compound that can form a stable protective film on the positive electrode active material by charging and discharging, but the use of a chain disulfonic acid ester in the initial cycle (cycle number: 1 to 5 times) It is preferable from the viewpoint that a protective film is stably formed on the positive electrode active material at this stage. Moreover, although the negative electrode film is formed by a reduction reaction, the positive electrode film is considered to be formed by deprotonation. Therefore, the additive is preferably a chain disulfonic acid ester whose terminal is a carbon-carbon double bond. The chain disulfonic acid ester having a carbon-carbon double bond at the end is preferably a chain disulfonic acid ester having both ends at a carbon-carbon double bond. Examples of the chain disulfonic acid ester whose both ends are carbon-carbon double bonds include a compound represented by the following formula (3).
Figure JPOXMLDOC01-appb-C000001
 　また、鎖状ジスルホン酸エステルは、ベンゼン環等の立体的に大きな構造を含まないことが好ましい。
Figure JPOXMLDOC01-appb-C000001
 The chain disulfonic acid ester preferably does not contain a sterically large structure such as a benzene ring.
　電解液中に含まれる添加剤の量は、電解液の質量に対して添加剤が１質量％以上、５質量％以下であることが好ましい。５質量％以下であることにより、添加剤を電解液中に十分溶解させることができ、電解液の粘性を低くすることができる。電解液中に含まれる添加剤の量は、十分な皮膜効果が得られる観点から、電解液の質量に対して添加剤が１．５質量％以上、４質量％以下であることがより好ましく、２質量％以上、３質量％以下であることがさらに好ましい。 The amount of the additive contained in the electrolytic solution is preferably 1% by mass or more and 5% by mass or less based on the mass of the electrolytic solution. By being 5 mass% or less, an additive can fully be dissolved in electrolyte solution and the viscosity of electrolyte solution can be made low. From the viewpoint of obtaining a sufficient film effect, the amount of the additive contained in the electrolytic solution is more preferably 1.5% by mass or more and 4% by mass or less based on the mass of the electrolytic solution. More preferably, it is 2 mass% or more and 3 mass% or less.
　また、電解液に、負極における保護皮膜が形成され易い環式スルホン酸エステルをさらに混合してもよい。前記添加剤と環式スルホン酸エステルとの混合比率は特に限定されないが、両者の総量が電解液に対し５質量％を超えない範囲で添加することが好ましい。なお、環式スルホン酸エステル単独では正極における保護皮膜は形成されにくいため、十分な効果は得られない。 Further, a cyclic sulfonic acid ester that easily forms a protective film on the negative electrode may be further mixed with the electrolytic solution. The mixing ratio of the additive and the cyclic sulfonic acid ester is not particularly limited, but it is preferable to add them in a range in which the total amount of both does not exceed 5% by mass with respect to the electrolytic solution. In addition, since the protective film in a positive electrode is hard to be formed only with cyclic sulfonate ester, sufficient effect is not acquired.
　本実施形態に係る二次電池は、正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成されている。該化合物が正極活物質の表面に形成されていることにより、充放電過程におけるマンガンの溶出が大幅に抑制され、電解液の酸化分解が抑制される。該化合物は、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６．５ｅＶ以上、２４７８．９ｅＶ以下の範囲にピークを有することが好ましく、２４７７ｅＶ以上、２４７８．７ｅＶ以下の範囲にピークを有することがより好ましく、２４７７．５ｅＶ以上、２４７８．５ｅＶ以下の範囲にピークを有することがさらに好ましい。なお、正極活物質の表面とは、正極活物質の最表面から深さ方向に１００ｎｍの領域を示す。 In the secondary battery according to this embodiment, a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material. By forming the compound on the surface of the positive electrode active material, elution of manganese in the charge / discharge process is significantly suppressed, and oxidative decomposition of the electrolytic solution is suppressed. The compound preferably has a peak in the range of 2476.5 eV or more and 2478.9 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur, and may have a peak in the range of 2477 eV or more and 2478.7 eV or less. More preferably, it has a peak in the range of 2477.5 eV or more and 2478.5 eV or less. Note that the surface of the positive electrode active material indicates a region of 100 nm in the depth direction from the outermost surface of the positive electrode active material.
　硫黄のＫ吸収端Ｘ線吸収微細構造（ＸＡＦＳ）（Ｘ－ｒａｙ　Ａｂｓｏｒｐｔｉｏｎ　Ｆｉｎｅ　Ｓｔｒｕｃｔｕｒｅ）スペクトルの測定方法について以下に示す。硫黄のＫ吸収端ＸＡＦＳスペクトルは、高エネルギー加速器研究機構物質構造科学研究所放射光科学研究施設（Ｐｈｏｔｏｎ　Ｆａｃｔｏｒｙ）のビームライン９Ａ（軟Ｘ線モード）等のシンクロトロン放射光実験施設で測定した値である。 The measurement method of the K absorption edge X-ray absorption fine structure (XAFS) (X-ray Absorption Fine Structure) spectrum of sulfur is described below. The K absorption edge XAFS spectrum of sulfur was measured at synchrotron radiation experiment facilities such as the beam line 9A (soft X-ray mode) of the Synchrotron Radiation Science Research Facility (Photon Factory), Institute for Materials Structure Science, High Energy Accelerator Research Organization It is.
　偏向電磁石から放出される白色Ｘ線をＸ線分光器で単色化したＸ線を正極に照射して、試料から放出される蛍光Ｘ線及び二次電子のエネルギー依存性を測定することで、硫黄のＫ吸収端ＸＡＦＳスペクトルが得られる。本実施形態では、試料から放出される二次電子を検出する転換電子収量法を適用することで、試料の最表面から約１００ｎｍまでの深さの情報を得る。なお、試料から放出される蛍光Ｘ線を検出すれば、試料の最表面から約１μｍの深さの情報が得られる。 By irradiating the positive electrode with white X-rays emitted from the deflecting electromagnet and monochromatizing with an X-ray spectrometer, the energy dependence of the fluorescent X-rays and secondary electrons emitted from the sample is measured. The K absorption edge XAFS spectrum of is obtained. In this embodiment, by applying a conversion electron yield method for detecting secondary electrons emitted from the sample, information on the depth from the outermost surface of the sample to about 100 nm is obtained. If fluorescent X-rays emitted from the sample are detected, information about a depth of about 1 μm can be obtained from the outermost surface of the sample.
　得られたスペクトルのエネルギー位置の絶対値は、標準試料を元に決定することができる。本実施形態ではＮａ２ＳＯ４を標準試料として用い、Ｎａ２ＳＯ４のピーク位置を２４８０ｅＶとしてエネルギー校正を行う。本実施形態における硫黄のＫ吸収端ＸＡＦＳスペクトルのピーク強度の最大値を示すエネルギー位置は、Ｎａ２ＳＯ４のピークの強度の最大値を示すエネルギー位置に対して、１ｅＶ以上、２ｅＶ以下低エネルギー側に位置していることが好ましく、１．１ｅＶ以上、１．９ｅＶ以下低エネルギー側に位置していることがより好ましく、１．２ｅＶ以上、１．８ｅＶ以下低エネルギー側に位置していることがさらに好ましく、１．３ｅＶ以上、１．７ｅＶ以下低エネルギー側に位置していることが特に好ましい。 The absolute value of the energy position of the obtained spectrum can be determined based on a standard sample. In this embodiment, Na 2 SO 4 is used as a standard sample, and the energy calibration is performed with the peak position of Na 2 SO 4 being 2480 eV. The energy position indicating the maximum value of the peak intensity of the sulfur K absorption edge XAFS spectrum in the present embodiment is 1 eV or more and 2 eV or less on the low energy side with respect to the energy position indicating the maximum value of the peak intensity of Na 2 SO 4. It is preferably located at a low energy side of 1.1 eV or more and 1.9 eV or less, more preferably 1.2 eV or more and 1.8 eV or less. More preferably, it is particularly preferably 1.3 eV or more and 1.7 eV or less on the low energy side.
　なお、ＸＡＦＳスペクトルのピーク強度は、対応する化学種の存在量に対応することから、保護皮膜の量を推定することができる。また、保護皮膜による電解液成分の酸化分解抑制効果を確認するため、リンのＫ吸収端でも正極のＸＡＦＳ測定を行うことができる。この測定方法は硫黄のＫ吸収端ＸＡＦＳ測定と同様である。また、マンガンの溶出量の測定については、負極に析出したマンガンについて波長分散型の蛍光Ｘ線分析装置を用いて定量することで、測定することができる。 In addition, since the peak intensity of the XAFS spectrum corresponds to the abundance of the corresponding chemical species, the amount of the protective film can be estimated. Moreover, in order to confirm the oxidative decomposition inhibitory effect of the electrolyte component by a protective film, the XAFS measurement of a positive electrode can be performed also at the K absorption edge of phosphorus. This measurement method is the same as the measurement of sulfur K absorption edge XAFS. Moreover, about the measurement of the elution amount of manganese, it can measure by quantifying the manganese deposited on the negative electrode using a wavelength dispersion type fluorescent X-ray analyzer.
　また、ＸＡＦＳスペクトルにおけるピークの特定は以下の方法により行うことができる。
（１）測定データの２階微分からピーク位置を特定する。
（２）測定データからバックグラウンドを引く。
（関数：Ａ＊ａｔａｎ（（ｘ－ｘ０）／ａ）＋１／２）、ａはスペクトルの分解能である。）
（３）（２）の関数を（１）のピーク位置の複数関数でフィッティングする。
（関数はローレンツ関数、Ｐｓｅｕｄｏ－ｖｏｉｇｔ関数が一般的である。）
（４）（３）の半値幅がスペクトルの分解能（励起寿命）以下の場合はノイズと判定する。 The peak in the XAFS spectrum can be specified by the following method.
(1) The peak position is specified from the second derivative of the measurement data.
(2) Subtract the background from the measurement data.
(Function: A * atan ((x−x0) / a) +1/2), a is the spectral resolution. )
(3) The function of (2) is fitted with a plurality of functions of the peak position of (1).
(Functions are generally Lorentz functions and Pseudo-voice functions.)
(4) When the half width of (3) is less than the spectral resolution (excitation lifetime), it is determined as noise.
　本実施形態に係る二次電池の形状は、特に制限はないが、例えば、角形、ペーパー型、積層型、円筒型、コイン型、ラミネート外装型等の種々の形状を採用することができる。 The shape of the secondary battery according to the present embodiment is not particularly limited, but various shapes such as a square shape, a paper shape, a laminated shape, a cylindrical shape, a coin shape, and a laminated exterior shape can be employed.
　本実施形態に係る二次電池の製造方法は、リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える充放電前二次電池を組み立てる工程と、前記充放電前二次電池を充放電する工程と、を含み、前記充放電により、前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成される。 A method for manufacturing a secondary battery according to the present embodiment includes a lithium salt, an electrolyte solution containing a non-aqueous solvent capable of dissolving the lithium salt, and an additive, and a positive electrode containing a positive electrode active material capable of inserting and removing lithium. And a step of assembling a pre-charge / discharge secondary battery comprising a negative electrode and a step of charging / discharging the pre-charge / discharge secondary battery, and the charge / discharge causes sulfur K absorption on the surface of the positive electrode active material. A compound having a peak in the range of 2476 eV or more and 2479 eV or less in the edge X-ray absorption fine structure spectrum is formed.
　例えば、図１に示す二次電池において、乾燥空気又は不活性ガス雰囲気下、正極１５及び負極１６を、セパレータ１７を介して積層し、積層電極体を作製する。該積層電極体は捲回されていてもよい。該積層電極体を電池缶や、合成樹脂と金属箔との積層体からなる可とう性フィルム等の外装体（不図示）に収容する。その後、外装体内に電解液を注ぎ、積層電極体に電解液を含浸させ、外装体を封止する。これにより、充放電前二次電池を作製する。 For example, in the secondary battery shown in FIG. 1, a positive electrode 15 and a negative electrode 16 are laminated via a separator 17 in a dry air or inert gas atmosphere to produce a laminated electrode body. The laminated electrode body may be wound. The laminated electrode body is accommodated in a battery can or an exterior body (not shown) such as a flexible film made of a laminated body of synthetic resin and metal foil. Thereafter, an electrolytic solution is poured into the exterior body, the laminated electrode body is impregnated with the electrolytic solution, and the exterior body is sealed. Thereby, the secondary battery before charging / discharging is produced.
　次に、前記充放電前二次電池を充放電することにより、負極及び正極上に添加剤由来の保護皮膜が形成され、本実施形態に係る二次電池が得られる。正極の正極活物質上に形成される保護皮膜には、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が含まれる。これにより、充放電サイクルにおけるマンガンの溶出が大幅に抑制され、電解液の酸化分解が抑制される。なお、前記充放電は外装体を封止する前に行ってもよい。 Next, by charging / discharging the pre-charge / discharge secondary battery, a protective film derived from the additive is formed on the negative electrode and the positive electrode, and the secondary battery according to this embodiment is obtained. The protective film formed on the positive electrode active material of the positive electrode includes a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur. Thereby, elution of manganese in the charge / discharge cycle is significantly suppressed, and oxidative decomposition of the electrolytic solution is suppressed. In addition, you may perform the said charging / discharging before sealing an exterior body.
　以下、本実施形態を実施例によりさらに詳細に説明するが、本実施形態はこれらに限定されない。 Hereinafter, the present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to these.
　［実施例１］
　（充放電前二次電池の作製）
　正極活物質（ＬｉＭｎ２Ｏ４：ＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２＝４：１（質量比））および導電性付与剤としてのカーボンブラックを乾式混合した。該混合物を、バインダーであるＰＶＤＦを溶解させたＮＭＰ中に均一に分散させて、スラリーを作製した。該スラリーを正極集電体であるアルミニウム金属箔（厚さ２０μｍ）上に塗布した。その後、ＮＭＰを蒸発させることにより正極を作製した。正極中の固形分比率は、正極活物質：導電性付与剤：ＰＶＤＦ＝９０：５：５（質量％）であった。 [Example 1]
(Preparation of secondary battery before charge / discharge)
A positive electrode active material (LiMn 2 O 4 : LiNi 0.8 Co 0.15 Al 0.05 O 2 = 4: 1 (mass ratio)) and carbon black as a conductivity-imparting agent were dry mixed. The mixture was uniformly dispersed in NMP in which PVDF as a binder was dissolved to prepare a slurry. The slurry was applied on an aluminum metal foil (thickness 20 μm), which was a positive electrode current collector. Then, the positive electrode was produced by evaporating NMP. The solid content ratio in the positive electrode was positive electrode active material: conductivity imparting agent: PVDF = 90: 5: 5 (mass%).
　負極活物質である炭素材料（カーボン：ＰＶＤＦ＝９５：５（質量％））をＮＭＰ中に分散させ、負極集電体である銅箔（厚さ１０μｍ）上に塗布した。その後、ＮＭＰを蒸発させることにより負極を作製した。 A carbon material (carbon: PVDF = 95: 5 (mass%)) as a negative electrode active material was dispersed in NMP and applied on a copper foil (thickness 10 μm) as a negative electrode current collector. Then, the negative electrode was produced by evaporating NMP.
　支持塩としてのＬｉＰＦ６と、ＥＣ／ＤＥＣ溶媒（ＥＣ：ＤＥＣ＝３０：７０（体積比））と、添加剤としての末端が炭素－炭素二重結合の鎖状ジスルホン酸エステルである前記式（３）で示される化合物とを混合し、電解液を調製した。電解液中のＬｉＰＦ６の濃度は１ｍｏｌ／Ｌであった。また、電解液中の鎖状ジスルホン酸エステルの濃度は、電解液の質量に対して２質量％であった。 LiPF 6 as a supporting salt, an EC / DEC solvent (EC: DEC = 30: 70 (volume ratio)), and the above formula (Terminal as a additive) is a chain disulfonic acid ester having a carbon-carbon double bond ( The compound shown by 3) was mixed to prepare an electrolytic solution. The concentration of LiPF 6 in the electrolytic solution was 1 mol / L. Moreover, the density | concentration of the chain | strand-shaped disulfonic acid ester in electrolyte solution was 2 mass% with respect to the mass of electrolyte solution.
　前記正極と前記負極とをポリエチレンからなるセパレータを介して積層し、積層電極体を作製した。該積層電極体をアルミラミネートで包み込み、アルミラミネートの周囲の３辺を熱融着した。最後の１辺を熱融着する前に、前記電解液をアルミラミネート内に注ぎ、電解液を積層電極体に含浸させた。その後、最後の１辺を熱融着することにより、充放電前二次電池を作製した。 The positive electrode and the negative electrode were laminated via a polyethylene separator to produce a laminated electrode body. The laminated electrode body was wrapped with aluminum laminate, and the three sides around the aluminum laminate were heat-sealed. Before heat-sealing the last side, the electrolyte solution was poured into an aluminum laminate, and the laminated electrode body was impregnated with the electrolyte solution. Then, the secondary battery before charging / discharging was produced by heat-seal | fusing the last 1 side.
　（サイクル試験）
　作製した充放電前二次電池に対し、充放電レート１Ｃで充電終止電圧４．２Ｖ、放電終止電圧３Ｖの条件にてサイクル試験を行った。充放電のサイクル数は１回、１００回、１０００回の３種類とした。なお、初回（１回目）の充放電により、正極及び負極に前記鎖状ジスルホン酸エステルに由来する保護皮膜が形成される。 (Cycle test)
A cycle test was conducted on the manufactured secondary battery before charge and discharge under the conditions of a charge end voltage of 4.2 V and a discharge end voltage of 3 V at a charge / discharge rate of 1C. The number of charge / discharge cycles was 1, 100 and 1000. In addition, the protective film derived from the said chain | strand-shaped disulfonic acid ester is formed in a positive electrode and a negative electrode by the charging / discharging of the first time (1st time).
　（容量維持率）
　前記サイクル試験を１回行った後の放電容量に対する、前記サイクル試験を１０００回行った後の放電容量の割合を容量維持率として算出した。 (Capacity maintenance rate)
The ratio of the discharge capacity after 1000 cycles of the cycle test to the discharge capacity after 1 cycle test was calculated as the capacity retention rate.
　（硫黄のＫ吸収端ＸＡＦＳスペクトル測定）
　１回のサイクル試験後、二次電池をグローボックス内で解体し、正極をＤＥＣで十分洗浄した。その後、該正極を分析用試料として１ｃｍ×１ｃｍのサイズに切り出した。該分析用試料をラミネートパックに封止後、該分析用試料について高エネルギー加速器研究機構ＢＬ－９Ａにて硫黄のＫ吸収端でＸＡＦＳ測定を行った。なお、正極活物質中には不純物としてＳＯ４成分が存在するため、表面転換電子収量法を用いて表面のみの情報を取り出した。また、エネルギー校正を行うために、標準試料としてＮａ２ＳＯ４の粉末試料をペレット状に成形して、硫黄のＫ吸収端にて同様にＸＡＦＳ測定を行った。結果を図２に示す。 (Sulfur K absorption edge XAFS spectrum measurement)
After one cycle test, the secondary battery was disassembled in a glow box, and the positive electrode was sufficiently washed with DEC. Thereafter, the positive electrode was cut into a size of 1 cm × 1 cm as an analysis sample. The analytical sample was sealed in a laminate pack, and then the XAFS measurement was performed on the analytical sample at the sulfur K absorption edge using the high energy accelerator research organization BL-9A. Since the SO 4 component is present as an impurity in the positive electrode active material, information on only the surface was extracted using the surface conversion electron yield method. In addition, in order to perform energy calibration, a Na 2 SO 4 powder sample was formed into a pellet as a standard sample, and XAFS measurement was similarly performed at the sulfur K absorption edge. The results are shown in FIG.
　（リンのＫ吸収端ＸＡＦＳスペクトル測定）
　１回及び１００回のサイクル試験後、正極をＤＥＣで十分洗浄した。その後、該正極を分析用試料として１ｃｍ×１ｃｍのサイズに切り出した。該分析用試料をラミネートパックに封止後、該分析用試料について高エネルギー加速器研究機構ＢＬ－９ＡにてリンのＫ吸収端でＸＡＦＳ測定を行った。なお、正極活物質中には不純物としてＳＯ４成分が存在するため、表面転換電子収量法を用いて表面のみの情報を取り出した。結果を図３に示す。 (Measurement of phosphorus K absorption edge XAFS spectrum)
After the 1st and 100th cycle tests, the positive electrode was thoroughly washed with DEC. Thereafter, the positive electrode was cut into a size of 1 cm × 1 cm as an analysis sample. After sealing the analytical sample in a laminate pack, XAFS measurement was performed on the analytical sample at the K absorption edge of phosphorus using the High Energy Accelerator Research Organization BL-9A. Since the SO 4 component is present as an impurity in the positive electrode active material, information on only the surface was extracted using the surface conversion electron yield method. The results are shown in FIG.
　（蛍光Ｘ線分析（ＸＲＦ））
　１０００回のサイクル試験後、負極をＤＥＣで十分洗浄した。その後、該負極を分析用試料として１ｃｍ×１ｃｍのサイズに切り出した。ラミネートパックに封止後、該分析用試料について蛍光Ｘ線分析装置（Ｒｈ　Ｋα線、６０ｋＶ　６６ｍＡ、分光結晶ＬｉＦ（２００）、パナリティカル製）を用いてマンガンの定量分析を行った。 (X-ray fluorescence analysis (XRF))
After 1000 cycle tests, the negative electrode was thoroughly washed with DEC. Thereafter, the negative electrode was cut into a size of 1 cm × 1 cm as a sample for analysis. After sealing in a laminate pack, the analysis sample was subjected to a quantitative analysis of manganese using a fluorescent X-ray analyzer (Rh Kα ray, 60 kV 66 mA, spectral crystal LiF (200), manufactured by Panalical).
　［比較例１］
　添加剤として、末端がベンゼン環の鎖状ジスルホン酸エステルである下記式（４）で示される化合物を用いて電解液を調製した以外は実施例１と同様に充放電前二次電池を作製し、サイクル試験、各種測定を行った。 [Comparative Example 1]
A secondary battery before charge / discharge was prepared in the same manner as in Example 1 except that an electrolyte was prepared using a compound represented by the following formula (4) whose terminal is a chain disulfonic acid ester having a benzene ring as an additive. A cycle test and various measurements were performed.
Figure JPOXMLDOC01-appb-C000002
 　硫黄のＫ吸収端でのＸＡＦＳ測定の結果を図２に、リンのＫ吸収端でのＸＡＦＳ測定の結果を図３に示す。
Figure JPOXMLDOC01-appb-C000002
 FIG. 2 shows the result of XAFS measurement at the sulfur K absorption edge, and FIG. 3 shows the result of XAFS measurement at phosphorus K absorption edge.
　図２に示すように、硫黄のＫ吸収端ＸＡＦＳ測定において、比較例１では２４８０ｅＶ付近に小さなピークが観測されたのに対して、実施例１では２４７６ｅＶ以上、２４７９ｅＶ以下の範囲に鋭いピークが観測された。また、実施例１のピークの強度の最大値を示すエネルギー位置は、標準試料Ｎａ２ＳＯ４のピークの強度の最大値を示すエネルギー位置に対して１．５ｅＶ低エネルギー側に位置していることが確認された。なお、ＸＰＳでは両者とも１６０ｅＶ付近にブロードなピークを形成しており、明確な差は認められなかった。 As shown in FIG. 2, in the K absorption edge XAFS measurement of sulfur, a small peak was observed in the vicinity of 2480 eV in Comparative Example 1, whereas a sharp peak was observed in the range of 2476 eV to 2479 eV in Example 1. It was done. Moreover, the energy position which shows the maximum value of the peak intensity of Example 1 is located on the lower energy side by 1.5 eV with respect to the energy position which shows the maximum value of the peak intensity of the standard sample Na 2 SO 4 . Was confirmed. In XPS, a broad peak was formed in the vicinity of 160 eV, and no clear difference was observed.
　図３はリンのＫ吸収端ＸＡＦＳスペクトル測定の結果であり、電解液の主成分であるリンのＫ吸収端でＸＡＦＳ測定を行うことで、電解液の分解状態を調べた。図３において、２１５５～２１６０ｅＶに存在するピークＢは、電解液に含まれる支持塩であるトリフルオロリン酸（ＰＦ６）に対応する。また、２１５０～２１５５ｅＶに存在するピークＡは、電解液中のＰＦ６が分解して生成したフッ化度の低下したＰＯＦ３等に対応する。 FIG. 3 shows the results of measurement of the phosphorus K absorption edge XAFS spectrum. The decomposition state of the electrolyte was examined by performing XAFS measurement at the phosphorus K absorption edge, which is the main component of the electrolyte. In FIG. 3, the peak B existing at 2155 to 2160 eV corresponds to trifluorophosphoric acid (PF 6 ) which is a supporting salt contained in the electrolytic solution. The peak A existing at 2150 to 2155 eV corresponds to POF 3 having a reduced degree of fluorination produced by decomposition of PF 6 in the electrolytic solution.
　１００サイクル後の前記ピークＡと前記ピークＢとの強度比（Ａ／Ｂ）を表１に示す。硫黄のＫ吸収端ＸＡＦＳ測定において、２４７６～２４７９ｅＶにピークが存在しない比較例１では、電解液中のＰＦ６の分解成分由来のピークであるピークＡの割合が高い。一方、２４７６～２４７９ｅＶにピークが存在する実施例１では、電解液中のＰＦ６の分解成分由来のピークであるピークＡの割合が低い。したがって、硫黄のＫ吸収端ＸＡＦＳ測定において、２４７６～２４７９ｅＶにピークを有する化合物が正極活物質の表面に形成された正極を備える二次電池では、電池特性の低下原因である電解液の分解反応が大幅に抑制されることが確認された。 Table 1 shows the intensity ratio (A / B) between the peak A and the peak B after 100 cycles. In Comparative Example 1 where no peak exists at 2476 to 2479 eV in the measurement of sulfur K absorption edge XAFS, the ratio of peak A, which is a peak derived from the decomposition component of PF 6 in the electrolyte, is high. On the other hand, in Example 1 in which peaks exist at 2476 to 2479 eV, the ratio of peak A, which is a peak derived from the decomposition component of PF 6 in the electrolyte, is low. Therefore, in the secondary battery having a positive electrode in which a compound having a peak at 2476 to 2479 eV is formed on the surface of the positive electrode active material in sulfur K absorption edge XAFS measurement, the decomposition reaction of the electrolytic solution, which is a cause of deterioration of battery characteristics, is caused. It was confirmed that it was significantly suppressed.
Figure JPOXMLDOC01-appb-T000003
 　また、負極におけるマンガン析出量をＸＲＦで測定した結果、実施例１と比較例１とのマンガンの強度比（実施例１／比較例１）は０．８６であった。したがって、実施例１の方が比較例１よりも負極におけるマンガンの析出量、すなわち正極からのマンガン溶出量が低減していることが確認された。なお、マンガン溶出量は微量であるため、１０００サイクル後の試料を測定に用い、かつ両者の強度比で比較した。
Figure JPOXMLDOC01-appb-T000003
 Moreover, as a result of measuring the manganese precipitation amount in a negative electrode by XRF, the intensity ratio (Example 1 / Comparative Example 1) of manganese of Example 1 and Comparative Example 1 was 0.86. Therefore, it was confirmed that the amount of precipitation of manganese in the negative electrode, that is, the amount of manganese elution from the positive electrode was reduced in Example 1 compared to Comparative Example 1. In addition, since the amount of manganese elution was very small, a sample after 1000 cycles was used for measurement, and the strength ratio of the two was compared.
　さらに、容量維持率を算出した結果を表２に示す。実施例１は比較例１よりも容量維持率が高いことが確認された。前述したように実施例１では正極からのマンガンの溶出が抑制されており、電解液成分の酸化分解が低減されたためと考えられる。 Furthermore, Table 2 shows the results of calculating the capacity maintenance rate. It was confirmed that Example 1 had a higher capacity retention rate than Comparative Example 1. As described above, in Example 1, the elution of manganese from the positive electrode is suppressed, which is considered to be because the oxidative decomposition of the electrolytic solution component is reduced.
　以上、本実施形態によれば、マンガンの溶出を大幅に低減することでサイクル特性を向上させた二次電池を提供することができる。 As described above, according to the present embodiment, it is possible to provide a secondary battery with improved cycle characteristics by significantly reducing manganese elution.
　この出願は、２０１２年６月１１日に出願された日本出願特願２０１２－１３１７１１を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2012-131711 filed on June 11, 2012, the entire disclosure of which is incorporated herein.
　以上、実施形態及び実施例を参照して本願発明を説明したが、本願発明は上記実施形態及び実施例に限定されるものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。 As mentioned above, although this invention was demonstrated with reference to embodiment and an Example, this invention is not limited to the said embodiment and Example. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
１１　　正極集電体
１２　　正極活物質含有層
１３　　負極集電体
１４　　負極活物質含有層
１５　　正極
１６　　負極
１７　　セパレータ DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12 Positive electrode active material content layer 13 Negative electrode collector 14 Negative electrode active material content layer 15 Positive electrode 16 Negative electrode 17 Separator

Claims (8)

  1. 　リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える二次電池であって、
    　前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成されている二次電池。     A secondary battery comprising a lithium salt, an electrolyte solution containing a non-aqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium, and a negative electrode,
    A secondary battery in which a compound having a peak in the range of 2476 eV or more and 2479 eV or less in the K absorption edge X-ray absorption fine structure spectrum of sulfur is formed on the surface of the positive electrode active material.
  2. 　前記ピークの強度の最大値を示すエネルギー位置が、Ｎａ２ＳＯ４のピークの強度の最大値を示すエネルギー位置に対して、１ｅＶ以上、２ｅＶ以下低エネルギー側に位置している請求項１に記載の二次電池。 The energy position indicating the maximum value of the peak intensity is located on the lower energy side by 1 eV or more and 2 eV or less with respect to the energy position indicating the maximum value of the peak intensity of Na 2 SO 4. Secondary battery.
  3. 　前記正極活物質がマンガンを含む請求項１又は２に記載の二次電池。 The secondary battery according to claim 1 or 2, wherein the positive electrode active material contains manganese.
  4. 　前記正極活物質が、下記式（１）
    　　Ｌｉ１＋ｘＭｎ２Ｏ４＋δ　　（１）
    （式（１）において、０≦ｘ＜０．２、０≦δ＜０．３である。）
    で示される化合物と、
    　下記式（２）
    　　ＬｉＮｉ１－α－βＣｏαＭβＯ２　　（２）
    （式（２）において、ＭはＡｌ及びＭｎの少なくとも一方を含む。０．１０≦α≦０．４７、０．０３≦β≦０．４、０．１３≦α＋β≦０．５０である。）
    で示される化合物とを含む請求項３に記載の二次電池。     The positive electrode active material has the following formula (1)
    Li 1 + x Mn 2 O 4 + δ (1)
    (In formula (1), 0 ≦ x <0.2 and 0 ≦ δ <0.3.)
    A compound represented by
    Following formula (2)
    LiNi 1-α-β Co α M β O 2 (2)
    (In the formula (2), M includes at least one of Al and Mn. 0.10 ≦ α ≦ 0.47, 0.03 ≦ β ≦ 0.4, 0.13 ≦ α + β ≦ 0.50. )
    The secondary battery of Claim 3 containing the compound shown by these.
  5. 　前記添加剤が鎖状ジスルホン酸エステルである請求項１から４のいずれか１項に記載の二次電池。 The secondary battery according to any one of claims 1 to 4, wherein the additive is a chain disulfonic acid ester.
  6. 　前記鎖状ジスルホン酸エステルの末端が炭素－炭素二重結合である請求項５に記載の二次電池。 The secondary battery according to claim 5, wherein a terminal of the chain disulfonic acid ester is a carbon-carbon double bond.
  7. 　前記電解液が、前記電解液の質量に対して前記添加剤を１質量％以上、５質量％以下含む請求項１から６のいずれか１項に記載の二次電池。 The secondary battery according to any one of claims 1 to 6, wherein the electrolyte contains 1% by mass or more and 5% by mass or less of the additive with respect to the mass of the electrolyte.
  8. 　リチウム塩、該リチウム塩を溶解可能な非水溶媒及び添加剤を含む電解液と、リチウムを挿入、脱離可能な正極活物質を含む正極と、負極とを備える充放電前二次電池を組み立てる工程と、
    　前記充放電前二次電池を充放電する工程と、を含む二次電池の製造方法であって、
    　前記充放電により、前記正極活物質の表面に、硫黄のＫ吸収端Ｘ線吸収微細構造スペクトルにおいて２４７６ｅＶ以上、２４７９ｅＶ以下の範囲にピークを有する化合物が形成される二次電池の製造方法。     Assembling a pre-charge / discharge secondary battery comprising an electrolyte containing a lithium salt, a nonaqueous solvent capable of dissolving the lithium salt and an additive, a positive electrode containing a positive electrode active material capable of inserting and removing lithium, and a negative electrode Process,
    Charging and discharging the secondary battery before charge and discharge, and a method of manufacturing a secondary battery,
    A method for producing a secondary battery, wherein a compound having a peak in the range of 2476 eV or more and 2479 eV or less in a sulfur K absorption edge X-ray absorption fine structure spectrum is formed on the surface of the positive electrode active material by the charge and discharge.
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